Novel processes for the production of useful intermediates

ABSTRACT

The present application relates to a new process for the asymmetric production of 3-(pyridin-4-yl)-3-hydroxy-pentanoic acid derivatives, which are useful intermediates in the manufacture of compounds that are known to show antiproliferative activity.

The present application relates to a new process for the production of 3-(pyridin-4-yl)-3-hydroxy-pentanoic acid derivatives.

In particular the present invention relates to a process for the production of the compounds of formula (I)

and pharmaceutically acceptable salts and esters thereof,

-   -   comprising     -   a) reacting a compound of formula (II),

-   -   with a compound of formula (III),

-   -   and     -   b) further reaction in the presence of alkali- or earth alkali         metal hydroxides to give the compounds of formula (I),     -   wherein         -   R and R¹ are independently, alkyl or benzyl, which benzyl is             optionally substituted by         -   one, two or three substituents independently selected from             -   —O-alkyl; alkyl and halogen; and     -   if R is alkyl, R¹ in formula (I) is also hydrogen or silyl, and         R¹ in formula (II) is also silyl;     -   R² is hydrogen or halogen;     -   X is

-   -   R³ and R⁴ are independently selected from hydrogen, phenyl,         alkyl and —C(CH₃)₂-phenyl;     -   R⁵ is phenyl, benzyl or alkyl;     -   R⁶ is hydrogen, alkyl or phenyl; and     -   R⁷ is hydrogen, methyl or phenyl; or alternatively     -   R⁵ and R⁶, together with the carbon atoms to which they are         attached form an indan-moiety and R⁷ is hydrogen;     -   R¹¹ and R¹² are independently alkyl, cycloalkyl, benzyl or         phenyl; and     -   R¹³ is phenyl or alkyl.

In a preferred embodiment, the present invention relates to a process for the production of the compounds of formula (I)

and pharmaceutically acceptable salts and esters thereof,

-   -   comprising     -   a) reacting a compound of formula (II),

-   -   with a compound of formula (III),

-   -   and     -   b) further reaction in the presence of alkali- or earth alkali         metal hydroxides to give the compounds of formula (I),     -   wherein         -   R and R¹ are independently alkyl or benzyl, which benzyl is             optionally substituted by one, two or three substituents             independently selected from         -   —O-alkyl; alkyl and halogen;     -   R² is hydrogen or halogen;     -   X is

-   -   R³ and R⁴ are independently selected from hydrogen, phenyl,         alkyl and —C(CH₃)₂-phenyl;     -   R⁵ is phenyl, benzyl or alkyl;     -   R⁶ is hydrogen, alkyl or phenyl; and     -   R⁷ is hydrogen, methyl or phenyl; or alternatively     -   R⁵ and R⁶, together with the carbon atoms to which they are         attached form an indan-moiety and R⁷ is hydrogen;     -   R¹¹ and R¹² are independently alkyl, cycloalkyl, benzyl or         phenyl; and     -   R¹³ is phenyl or alkyl.

In another preferred embodiment, the present invention relates to a process for the production of the compounds of formula (I)

and pharmaceutically acceptable salts and esters thereof,

-   -   comprising     -   a) reacting a compound of formula (II),

-   -   with a compound of formula (III),

-   -   and     -   b) further reaction in the presence of alkali- or earth alkali         metal hydroxides to give the compounds of formula (I),     -   wherein     -   R is alkyl; and     -   R¹ is hydrogen or silyl in formula (I) and silyl in formula         (II);     -   R² is hydrogen or halogen;     -   X is

-   -   R⁵ is phenyl, benzyl or alkyl;     -   R⁶ is hydrogen, alkyl or phenyl; and     -   R⁷ is hydrogen, methyl or phenyl.

The compounds of formula (I) are useful intermediates for the manufacture of homocamptothecins (hCPT's), some of which are known to show antiproliferative activity.

The alkaloid camptothecin (CPT, 1) shows potent antiproliferative activity and continues to serve as a very attractive lead structure for the development of new anti-cancer drugs (see e.g. in C. J. Thomas, N. J. Rahier, S. M. Hecht, Bioorg. Med. Chem. 2004, 12, 1585-1604). The structure of the pentacyclic skeleton contains a highly electrophilic α-hydroxy-δ-lactone ring (ring “E”), which rapidly hydrolyzes in basic and neutral media yielding the open chain carboxylate form (2, scheme 1), which is almost inactive.

This equilibrium is shifted toward the carboxylate form in human plasma thus explaining the lower efficacy of most CPT analogues in clinical trials.

The development of homocamptothecins (hCPT), which are CPT analogues possessing a seven membered β-hydroxy-ε-lactone ring “E”, addressed this issue. Although it was previously generally accepted that an α-hydroxylactone is an indispensable structural feature for anticancer activity, modifications of the CPT-lactone ring which retain the antiproliferative activity and, at the same time, displays enhanced stability against hydrolysis were investigated (Lavergne, Bigg et al., J. Med. Chem. 2000, 43, 2285-2289). Therefore hCPT provides an excellent template for the preparation of new, highly cytotoxic compounds, and two promising hCPT derivatives, 3 (Diflomotecan) and 4 (scheme 2), are under investigation for the treatment of cancer.

Processes for the manufacture of hCPT's are known in the art (U.S. Pat. No. 6,723,853 B2) principally following the general synthesis route given in scheme 3, wherein “X” and “Y” represent optional substituents (see also Lavergne, Bigg et al., J. Med. Chem. 2000, 43, 2285-2289).

However, when used in large scale manufacture (kg-amounts) these processes suffer from an extremely low yield of typically 0.5% of the bicyclic “DE-fragment”, which is essential for the biological activity in the final product. Therefore it remains the need to provide alternative synthesis routes of this fragment.

The solution provided by the present invention was found to be an asymmetric acetate aldol addition, leading to improved yields of the compounds of formula (I) which are is subsequently transformed into said “DE-fragment”, or its derivatives according to the nature of R² in formula (I). Acetate aldol addition reactions usually suffer from low enantioselectivities. Furthermore, asymmetric acetate aldol additions using ketone substrates are a largely unexplored field. Only few auxiliaries have been reported in literature to provide reasonable stereoselectivities in the addition reaction to acetophenone or similar phenylalkylketones (E. B. Dongala, D. L. Dull, C. Mioskowski, G. SoIIadié, Tetrahedron Lett. 1973, 4983-4986; M. Braun, R. Devant, Tetrahedron Lett. 1984, 5031-5034).

It has now surprisingly been found that said bicyclic “DE-fragment” can be obtained in an enantiomerically pure form (er of about 99.95:0.05) and in an overall yield of about 9%, starting from the compounds of formula (IV), scheme 5 and preferably from 2-chloro-4-cyanopyridine when using the process according to the present invention.

As used herein the term “silyl” means a group of the formula R¹⁴R¹⁵R¹⁶Si—, wherein R¹⁴, R¹⁵ and R¹⁶ are independently alkyl, cycloalkyl or phenyl. Preferred silyl groups are t-butyldimethylsilyl and t-butyldiphenylsilyl.

As used herein the term “alkyl” means a saturated, linear or branched hydrocarbon containing from 1 to 8, preferably 1 to 6 and more preferably 1 to 4 carbon atoms. Examples of such “alkyl” groups are methyl, ethyl, propyl, isopropyl, 1-butyl, 2-butyl, t-butyl and the like. In this connection the symbols “Me”, “Et” and “iPr” as used in the formulae herein mean a methyl-, ethyl- and isopropyl group respectively. In connection with the term “O-alkyl” as used herein the preferred “alkyl” is methyl.

As used herein the term “cycloalkyl” means a saturated mono- or bi-cyclic hydrocarbon consisting of 5 to 10 carbon-atoms. Preferred is a monocyclic hydrocarbon consisting of 5 to 7, more preferably of 6 carbon-atoms. Examples of such cycloalkyl groups are cyclopentyl, cyclohexyl, cycloheptyl, decahydro-naphthyl, octahydro-indyl and the like. According to the present invention, said cycloalkyl groups are unsubstituted or one, two, three or four times, preferably one or two times, substituted by phenyl, benzyl, alkyl, hydroxyl or oxo.

The term “heterocyclyl” as used herein means a mono-, bi- or tricyclic saturated or partially unsaturated or partially aromatic hydrocarbon, wherein one, two, three or four, preferably one or two carbon-atoms are replaced by oxygen, nitrogen or sulfur, preferably oxygen and nitrogen. Examples of such heterocyclic groups are 3,3a,4,8b-tetrahydro-1H-indeno[1,2-c]isoxazol-1-yl; 3,3a,8,8a-tetrahydro-1H-2-thia-3-aza-cyclopenta[a]inden-3-yl; octahydro-indol-1-yl; octahydro-benzo[c]isothiazol-1-yl; octahyciro-benzo[c]isoxazol-1-yl; 2,3-dihydro-1H-indol-1-yl; 1,3-dihydro-benzo[c]isothiazol-1-yl; 1,3-dihydro-benzo[c]isoxazol-1-yl and the like. According to the present invention, said heterocyclyl groups are unsubstituted or one, two, three or four times, preferably one or two times, substituted by phenyl, benzyl, alkyl, hydroxyl or oxo.

In the group “X” of formula (III) as used herein, when “R⁵ and R⁶ together with the carbon atoms to which they are attached form an indan-moiety”, said group X means

As used herein the term “alkali- or earth-alkali metal amide base” means lithium-, sodium-, potassium- and magnesium amide bases. Examples of such bases are lithium hexamethyldisilazane (LHMDS), lithium diisopropylamide (LDA), 1-lithium-2,2,6,6-tetramethylpiperidine (LTMP), lithium dicyclohexylamide (LiCA), sodium hexamethyldisilazane (NaHMDS), potassium hexamethyldisilazne (KHMDS). Especially preferred is the use of LHMDS.

As used herein the term “optionally substituted” means unsubstituted or one, two or three times substituted.

As used herein the term “ethereal solvents” means solvents from the chemical class of linear or cyclic ethers. Examples of such ethereal solvents are Diethylether (Et₂O), 1,2-dimethoxyethane (DME), diisopropylether (iPr₂O), tetrahydrofuran (THF) or tert-butyl methyl ether (TBME). Especially preferred is THF.

As used herein the term “mineral acids” means hydrochloric acid (HCl), hydrobromic acid (HBr), trimethylsilyl iodide (TMSI) or boron tribromide (BBr₃). Especially preferred is aqueous hydrobromic acid.

As used herein the term “room temperature” (RT) means ambient temperatures in the place where the process according to the present invention is carried out. Said temperatures may vary between 15 and 35° C. Preferably said temperature is between 18 and 28° C., more preferably between 20 and 23° C.

As used herein the term “pharmaceutically acceptable salts and esters” refers to conventional acid-addition salts- or base-addition salts of formula (I), or conventionally esterified compounds of formula (I) and are formed from suitable non-toxic organic or inorganic acids, organic or inorganic bases or from suitable alcohols respectively. Said “pharmaceutically acceptable salts and esters” may for example occur as intermediates during the process of the present invention before the compounds of formula (I) are isolated, or subsequent to their isolation before said compounds of formula (I) are further reacted to give the compounds of formula (A). Sample acid-addition salts include those derived from inorganic acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, sulfamic acid, phosphoric acid and nitric acid, and those derived from organic acids such as p-toluenesulfonic acid, salicylic acid, methanesulfonic acid, oxalic acid, succinic acid, citric acid, malic acid, lactic acid, fumaric acid, and the like. Sample base-addition salts include those derived from ammonium, potassium, sodium and quaternary ammonium hydroxides, such as for example, tetramethylammonium hydroxide.

Asymmetric acetate aldol additions using ketone substrates are a largely unexplored field. Very few is known about effective auxiliaries, which are the key factor in order to achieve high selectivities in this type of reaction. It has now been found that good selectivities were obtained with auxiliaries of formula (III), bearing bulky groups in R⁵ and R³ of the respective formulae as described below. According to the present invention the most promising auxiliaries are chiral oxazolidinones (acylated Evans type auxiliaries). The best selectivities were obtained with such chiral oxazolidinones bearing bulky groups in R⁵. A substituent R⁶ cis to R⁵ was shown to be advantageous both for conversion and selectivity, while a group R⁷ trans to R⁵ was shown to have a negative effect. Two auxiliaries are especially preferred according to the present invention: (4R)-4-tert-butyloxazolidin-2-one and (4R,5S)-4,5-diphenyloxazolidin-2-one.

The asymmetric aldol addition according to the present invention is usually carried out in the presence of alkali- or earthalkali metal bases. Preferred bases are lithium-, sodium-, potassium- and magnesium amide bases; lithium-, sodium- and potassium alkyl bases; sodium- and potassium aryl bases; and Grignard reagents. Examples of such bases are lithium hexamethyldisilazane (LHMDS), lithium diisopropylamide (LDA), 1-lithium-2,2,6,6,-tetramethylpiperidine (LTMP), lithium dicyclohexylamide (LiCA), sodium hexamethyldisilazane (NaHMDS), potassium hexamethyldisilazane (KHMDS), butyl lithium (BuLi) also in combination with alkali alkoxides, phenyl lithium (PhLi). Especially preferred is the use of LHMDS.

The process according to the present invention is preferably carried out in ethereal solvents or alkanes. Preferred examples of “ethereal solvents” are Diethylether (Et₂O), tetrahydrofuran (THF) or tert-butyl methyl ether (TBME). Preferred examples of alkanes are pentane, hexane or heptane as well as suitable derivatives thereof. The especially preferred solvent is THF.

The process according to the present invention is preferably carried out at temperatures from −120° C. to room temperature (RT). Especially preferred are temperatures from −100 to −60° C.

The subsequent auxialiary cleavage in order to obtain the compounds of formula (I) is carried out using ester- and/or amide cleavage methods well known to the skilled artisan as e.g. described in “T. W. Greene, P. G. M. Wuts, Protective Groups in Organic Synthesis, 3^(rd) edition, Wiley-Interscience 1999”. Preferably said auxiliary cleavage is carried out using metal alkoxides, for example alkali and earth alkali metal alkoxides. Especially preferred is the use of lithium hydroxide (LiOH) in combination with hydrogen peroxide (H₂O₂).

Subsequently, the conversion of the compounds of formula (I) into the above-mentioned “DE-fragment”, further referred to as the compounds of formula (A), is achieved using to conventional Lewis- or Broensted acid promoted ether cleavage methods, which are known to the skilled artisan and described e.g. in “T. W. Greene, P. G. M. Wuts, Protective Groups in Organic Synthesis, 3^(rd) edition, Wiley-Interscience 1999”. Preferred is the use of mineral acids like hydrochloric acid (HCl) or hydrobromic acid (HBr), trimethylsilyl iodide (TMSI), boron tribromide (BBr₃). Especially preferred is the method using aqueous hydrobromic acid. This reaction is preferably carried out in ethereal solvents like dimethoxyethane (DME), tetrahydrofuran (THF) or dioxane; or in nitriles like for example acetonitrile (MeCN) and at temperatures from 0 to 120° C., preferably from room temperature (RT) to 60° C.

The final reaction steps in order to obtain the compounds of formula (D) as described herein, especially Diflomotecan, from the compounds of formula (A) is known to the skilled artisan and can generally be performed according to the synthesis route described in scheme 4.

A preferred embodiment of the present invention is the process as described above, wherein X is

-   -   wherein         -   R⁵ is phenyl, benzyl, isopropyl, tert-butyl or methyl;         -   R⁶ is hydrogen, methyl or phenyl; and         -   R⁷ is hydrogen, methyl or phenyl; or alternatively         -   R⁵ and R⁶ together with the carbon atoms to which they are             attached, form an indan-moiety and         -   R⁷ is hydrogen.

Another preferred embodiment of the present invention is the process as described above, wherein

-   -   R¹ is benzyl;     -   R² is hydrogen; and     -   X is

-   -   wherein         -   R⁵ is phenyl, benzyl, isopropyl, tert-butyl or methyl;         -   R⁶ is hydrogen, methyl or phenyl; and         -   R⁷ is hydrogen, methyl or phenyl; or alternatively         -   R⁵ and R⁶ together with the carbon atoms to which they are             attached, form an indan-moiety and         -   R⁷ is hydrogen.

Another preferred embodiment of the present invention is the process as described above, wherein

-   -   R⁵ and R⁶ are both phenyl, and     -   R⁷ is hydrogen.

Another preferred embodiment of the present invention is the process as described above, wherein the compound of formula (I-1)

-   -   is obtained by     -   a) reacting the compound of formula (II-1)

-   -   with the compound of formula (III-1)

-   -   b) further reaction in the presence of lithiumhydroxide in         combination with hydrogen peroxide, to give the corresponding         compound of formula (I-1).

Another preferred embodiment of the present invention is the process as described above, wherein

-   -   R⁵ is phenyl, and     -   R⁶ and R⁷ are both hydrogen.

Another preferred embodiment of the present invention is the process as described above, wherein the compound of formula (I-2)

-   -   is obtained by     -   a) reacting the compound of formula (II-2)

-   -   with the compound of formula (III-2)

-   -   b) further reaction in the presence of lithiumhydroxide in         combination with hydrogen peroxide, to give the corresponding         compound of formula (I-2).

Yet another embodiment of the present invention is the process as described herein before, whereby the process step a) is carried out in the presence of an or earth-alkali metal amide base.

Yet another embodiment of the present invention is the process as described herein before, whereby the process step a) is carried out in the presence of lithium hexamethyldisilazane (LHMDS).

Yet another embodiment of the present invention is the process as described herein before, whereby the process step a) is carried out in the presence of diethylether (Et₂O), tetrahydrofuran (THF), tert-butyl methyl ether (TBME), pentane, hexane or heptane.

Yet another embodiment of the present invention is the process as described above, whereby the process step a) is carried out in the presence of tetrahydrofuran.

Yet another embodiment of the present invention is the process as described herein before, whereby the process step a) is carried out at temperatures in the range between 25° C. and −120° C.

Yet another embodiment of the present invention is the process as described above, whereby the process step a) is carried out at temperatures in the range between −60° C. and −100° C.

Yet another embodiment of the present invention is the process as described above, whereby the process step a) is carried out at temperatures between −90° C. and −100° C.

Yet another embodiment of the present invention is the process as described herein before, whereby the process step b) is carried out in the presence of an alkali- or earth alkali metal hydroxide, alone or in combination with hydrogen peroxide.

Yet another embodiment of the present invention is the process as described herein before, whereby the process step b) is carried out in the presence of lithium hydroxide in combination with hydrogen peroxide.

Yet another embodiment of the present invention is the process as described herein before, wherein X is

The compounds of formula (I), obtainable by the new process according to the present invention, are valuable intermediates for the manufacture of the homocamptothecins of formula (D). Some homocamptothecins, for example Diflomotecan, show antiproliferative activity and are therefore useful in the treatment and/or prevention of diseases related to abnormal cell proliferative activities, especially cancer.

Therefore, another embodiment of the present invention is the process as described above, wherein the compound of formula (I) is subsequently converted into a compound of formula (A)

in the presence of a mineral acid and an ethereal solvent at temperatures between room temperature (RT) and 60° C.

Still another embodiment of the present invention is the process as described above, wherein said compound of formula (A) is further reacted with a compound of formula (B)

in the presence of diisopropyl azodicarboxylate (DIAD), ethyldiphenylphosphine (EtPPh₂) and dimethylacetamide (DMA), to give a compound of formula (C)

Still another embodiment of the present invention is the process as described above, wherein said compound of formula (C) is further reacted in the presence of palladium (II) acetate (Pd(OAc)₂), potassium acetate (KOAc), triphenylphosphine (Ph₃P), tetrabutyl ammonium bromide (Bu₄NBr) and acetonitrile (MeCN) to give the corresponding compound of formula (D)

wherein

-   -   R² has the significance given herein before;     -   R⁸ and R⁹ are independently alkyl or halogen; and     -   R¹⁰ is 4-methyl-piperidin-1-ylmethyl or hydrogen.

Yet another embodiment of the present invention is the process as described above, wherein said compound of formula (I) is transformed into a compound of formula (D)

-   -   by:     -   a) converting said compound of formula (I) into a compound of         formula (A)

-   -   in the presence of a mineral acid and an ethereal solvent at         temperatures between room temperature (RT) and 60° C.; and     -   b) further reacting said compound of formula (A) with a compound         of formula (B)

-   -   in the presence of diisopropyl azodicarboxylate (DIAD),         ethyldiphenylphosphine (EtPPh₂) and dimethylacetamide (DMA), to         give a compound of formula (C)

-   -   and     -   c) said compound of formula (C) is further reacted in the         presence of palladium (II) acetate (Pd(OAc)₂), potassium acetate         (KOAc), triphenylphosphine (Ph₃P), tetrabutyl ammonium bromide         (Bu₄NBr) and acetonitrile (MeCN) to give the corresponding         compound of formula (D)

-   -   -   wherein         -   R² has the significance given herein before;         -   R⁸ and R⁹ are independently alkyl or halogen; and         -   R¹⁰ is 4-methyl-piperidin-1-ylmethyl or hydrogen.

Yet another embodiment of the present invention is the process as described above, wherein R² and R¹⁰ are both hydrogen, and R⁸ and R⁹ are both fluorine.

Still another embodiment of the present invention is the process as described above, wherein R² is hydrogen, R¹⁰ is 4-methyl-piperidin-1-ylmethyl, R⁸ is chlorine and R⁹ is methyl.

Still another embodiment of the present invention is the process as described above, wherein the process step a) is carried out in the presence of hydrobromic acid (HBr) and dimethoxyethane (DME) at temperatures between 45 and 55° C.

Still another embodiment of the present invention are the compounds of the general formula (I)

-   -   wherein         -   R and R¹ are independently alkyl, or benzyl, which benzyl is             optionally substituted by —O-alkyl; alkyl and halogen; and         -   if R is alkyl R¹ can also be hydrogen;         -   R² is hydrogen or halogen.

Still another embodiment of the present invention are the compounds of the general formula (I)

-   -   wherein         -   R and R¹ are independently alkyl or benzyl, which benzyl is             optionally substituted by —O-alkyl; alkyl and halogen; and         -   R² is hydrogen or halogen.

Still another embodiment of the present invention are the compounds as defined above, wherein

-   -   R² is halogen.

Still another embodiment of the present invention are the compounds as defined above, wherein

-   -   R and R¹ are independently alkyl or benzyl, which benzyl is         substituted by —O-alkyl; alkyl and halogen.

Still another embodiment of the present invention is the compound of formula (I)

-   -   (R)-3-(3-benzyloxymethyl-2-methoxy-pyridin-4-yl)-3-hydroxy-pentanoic         acid.

Still another embodiment of the present invention is the compound of formula (I)

-   -   (R)-3-Hydroxy-3-(3-hydroxymethyl-2-methoxy-pyridin-4-yl)-pentanoic         acid.

Still another embodiment of the present invention is the use of the compounds as defined above in the process as described herein before.

Still another embodiment of the present invention is the use of the compound

for the manufacture of the compounds represented by the formulae

Still another embodiment of the present invention is the use of the compound

for the manufacture of the compounds represented by the formulae

Still another embodiment of the present invention is the use of the process as described above for the preparation of the compounds of formula (I).

Still another embodiment of the present invention is the use of the process as described above in the manufacture of the compound with the formula

The compounds of formula (II), wherein R and R¹ are independently alkyl or optionally substituted benzyl and R² has the meaning given herein before, can be obtained by any process known to be applicable by the skilled artisan. According to the present invention the synthesis route as described in scheme 5 is especially preferred. Although being based on a known synthesis, the steps leading to the compounds of formula (II) were improved according to the present invention. This is because the purity of the ketones of formula (II) when obtained according to the known method, is not sufficient for the development of an asymmetric aldol addition reaction as described by the present invention. Especially the reaction conditions for steps 4 to 7 have been modified, resulting in higher yield and better quality of the ketones of formula (II), scheme 5.

Consequently the particular reaction conditions as described below for the reaction steps 1 to 7 of scheme 5 and in the accompanying non-limiting examples are a further embodiment of the present invention.

Steps 1 and 2:

These reactions are an alkanolysis of the starting material 2-chloro-4-cyano-pyridine, followed by a Grignard addition (step 2). Both reactions are well known to the skilled artisan. However, according to the present invention an amount between 0.5 to 3.0 equivalents (eq) sodium methoxide (NaOMe), preferably 1.0 to 1.5 eq, most preferably 1.0 to 1.2 eq, was used in step 1. The product is purified by soxhlet extraction. The following Grignard addition is preferably carried out in tert-butyl methyl ether (TBME) as to solvent.

Step 3:

During the acetal formation with propanediol, it was realized that the conversion strongly depends on the amount of acid catalyst used. In several cases, no conversion was realized even after 24 h with 2 mol % of para-toluenesulphonic acid (PTSA); however, with additional PTSA or sulfuric acid (H₂SO₄), the reaction was complete after 24 h. After these steps, the acetals of formula (VII) can be isolated in about 40% yield and with an HPLC purity >95% area after high vacuum distillation. These improvements are essential for the subsequent sensitive metalation of the pyridine 3-position.

Step 4:

In order to carry out the metalation of the pyridine 3-position we found that the concentration of an n-Butyllithium (n-BuLi) solution in hexane is a key parameter, which can be optimized instead of using the common 1.6 M n-BuLi in hexane solution. When using 1.7 to 4 M, preferably 2.0 to 3.0 M solutions of n-BuLi in hexane the amount of hexane, which is crucial for the solubility of mesithyl-lithium. (MesLi), can be reduced. The lithiated species was then trapped by dimethyl formamide (DMF) resulting in the aldehydes of formula (VIII), scheme 5. The advantages of this procedure are high conversions as well as the ease of product purification by silica gel filtration to remove mesityl side products and unreacted starting material as well as other side products. The most prominent side product was identified by LC-MS and NMR as mesityl addition product to the pyridine-6-position.

Step 5:

A reduction step with sodium borohydride (NaBH₄) is now required, thus providing the compounds of formula (IX), scheme 5 in high yield and purity after trituration with heptane.

Step 6:

In the subsequent benzylation step, it was desirable to replace sodium hydride (NaH), as used in the known procedure, by an alternative base. In addition to the safety issue, which is raised by NaH, we encountered formation of considerable amounts of high boiling dibenzyl ether as side product depending on the NaH quality. According to the present invention non-nucleophilic lithium bases are preferred. Especially preferred is lithium hexamethyl-disilazane (LHMDS), which is available as THF solution for clean preformation of the corresponding lithium alkoxide. By addition of 10 mol % of dry tetrabutylammonium iodide (TBAI), the alkylation proceeds without major decomposition at 65° C., furnishing the compounds of formula (X), scheme 5 in high purity. In order to remove excess of benzyl bromide, pyrrolidine was added after almost complete conversion and the resulting tertiary benzylamine was removed by extraction with aqueous hydrogen chloride (HCl). Surprisingly, the addition of pyrrolidine at the end of the reaction also resulted in an acceleration of benzylation of unreacted starting material (IX, scheme 5).

Step 7:

According to the present invention, the subsequent acetal cleavage is carried out utilizing a catalytic amount of para-toluenesulfonic acid (PTSA, 0.2 eq) in a mixture of Ethanol/water (4:1). Under these conditions, the crude ketones of formula (II) are isolated in high purity.

The compounds of formula (II), wherein R is alkyl, R¹ is silyl and R² has the meaning given herein before, can be obtained by any process known to be applicable by the skilled artisan. According to the present invention the synthesis route as described in scheme 6 is especially preferred in order to avoid the sophisticated use of mesityl-lithium (MesLi) and the related problems, such as the elaborate conditions for the in situ generation of MesLi and the formation of high boiling mesityl side products only removable by silica gel filtration.

Steps 1 and 2:

2-Methoxy-4-isopropylamides of formula (XIII) are prepared over two steps starting from 2-chloroisonicotinic acids of the formula (XI), which are first activated by formation of the corresponding acid chloride and then reacted in the same pot with isopropylamine. The 2-chloro substituent is subsequently substituted by a methoxy group using NaOMe.

Step 3:

Metalation of the 3-position of the compounds of formula (XIII) according to the present invention is preferably carried out with n-BuLi in the presence of TMEDA or lithium chloride (LiCl). Butyl addition to the pyridine-6-position was never observed for this substrate. While the regioselectivity is low in THF (3-Li/5-Li=ca. 3:1), metalation of the 3-position is significantly favored in TBME. The lithiated species is trapped by DMF yielding the N,O-hemiacetals of formula (XIV).

Step 4:

The crude product of step 3, which still, contains large amounts of DMF, is reduced by NaBH₄ in isopropanol/water to the corresponding hydroxyamide, which is then cyclized in the same pot by addition of aqueous HCl furnishing the lactones of formula (XV) which are purified by trituration. According to the present invention, the choice of an isopropanol/water mixture for this reduction step is especially preferred in order to reduce the amount of NaBH₄.

Step 5:

According to the present invention, the addition of ethyl to the lactones of formula (XV) to provide the lactols of formula (XVI) is preferably carried out using ethyllithium (EtLi). Especially preferred is the use of a combination of triethylaluminum (AlEt₃) and ethyllithium. Equimolar amounts of AlEt₃ and EtLi are pre-coordinated at 0° C. The solution of the starting material (XV) is then rapidly added at −40° C. In order to reach a high conversion, a second equivalent of EtLi is required, which is slowly added at −40° C., before the reaction mixture is allowed to slowly warm up to −15° C.

Step 6:

In order to obtain the ketone substrates of formula (II) for the asymmetric aldol addition reaction according to the present invention, the compound of formula (XVI) has to be opened by an appropriate electrophile. As a further feature of the present invention, silyl chlorides and especially t-butyldimethylsilyl-chloride (TBSCl) and t-butyldiphenylsilylchloride (TBDPSCl) are preferred. The workup of the TBS and TBDPS ether formation benefits from the heptane solubility of the lipophilic silyl ethers. As a result, the polar components DMF and imidazole were completely removed by aqueous workup and the crude ketones of formula (II) can be obtained in high purity.

The following examples and references are provided to aid the understanding of the present invention, the true scope of which is set forth in the appended claims. It is understood that modifications can be made in the procedures set forth without departing from the spirit of the invention.

In the following Examples, if not explicitly otherwise stated, analytical High Performance Liquid Chromatography (HPLC) was performed according to the following protocol:

Method SEVI.M Sample preparation: 5 μL of the reaction mixture were added to 0.2 mL acetonitrile/water (9:1). Equipment HP 1050 Series HPLC system Column Chromolith, Performance 100 × 4.6 Temperature 40° C. Mobile phase gradient (3 components A-C) A: water B: 800 ml water, 200 ml acetonitrile, 1 g TBAHS C: acetonitrile Flow 2.0 ml/min Injection volume 1 μl Detection UV 210 nm

EXAMPLE 1 Synthesis of 2-methoxy-isonicotinonitrile

A stirred suspension of 17.86 g NaOMe (330.7 mmol, 1.22 eq) in 95 mL acetonitrile was cooled to 0° C. and a solution of 37.56 g 2-chloro-4-cyano pyridine (8, 271.1 mmol) in 225 mL acetonitrile was added over 45 min. Stirring was continued at room temperature for 23 h until less than 4% (area) starting material were detected by HPLC. 11.1 g potassium dihydrogen phosphate (81.56 mmol, 0.30 eq) were added at 0° C. and stirring was continued for 3 h at room temperature. The reaction mixture was then evaporated to dryness in a rotary evaporator (40° C./10 mbar) yielding the crude product (64.94 g, 179% by weight) as a brown solid. 64.94 g crude product were extracted with 900 mL toluene for 18 h at reflux temperature using a soxhlet extraction apparatus yielding the title product (25.65 g, 71% by weight) as an orange solid.

Mp: 98° C.;

¹H NMR (300 MHz, CDCl₃): δ 8.31 (d, 1H, J=5.1 Hz), 7.07 (dd, 1H, J=5.1 Hz, J=1.2 Hz), 6.99 (br. s, 1H), 3.97 (s, 3H) ppm.

EXAMPLE 2 Synthesis of 1-(2-methoxy-pyridin-4-yl)-propan-1-one

A stirred suspension of 25.44 g of 2-methoxy-isonicotinonitrile as obtained in Example 1 (189.7 mmol) in 380 mL TBME was cooled to 0° C. and 114 mL ethyl magnesium chloride in THF(2.0 M, 228.0 mmol, 1.20 eq) were added within 45 min. Stirring was continued at 0° C. After 3 h 40 min, additional 5 mL ethyl magnesium chloride in THF(2.0 M, 10.0 mmol, 0.05 eq) were added at 0° C. The reaction was monitored by HPLC. After 4.5 h (<3% area 2-methoxy-isonicotinonitrile), the reaction was quenched at 0° C. by addition of 300 mL water. The resulting suspension was stirred for 16 h at room temperature and was then diluted with 200 mL toluene. The aqueous phase was extracted with 400 mL toluene and the combined organic phases were washed with 500 mL saturated aqueous NH₄Cl and 500 mL brine, dried over 50 g Na₂SO₄ (30 min) and filtered. The filter cake was washed with 100 mL toluene. After evaporation of solvent in a rotary evaporator (40° C./10 mbar), the title compound (28.64 g, 91% by weight) was obtained as an orange solid.

Mp: 38° C.;

¹H NMR (300 MHz, CDCl₃): δ 8.30 (d, 1H, J=5.3 Hz), 7.30 (dd, 1H, J=5.3 Hz, J=1.3), 7.18 (br. s, 1H), 3.98 (s, 3H), 2.96 (q, 2H, J=7.2 Hz), 1.22 (t, 3H, J=7.2 Hz) ppm

EXAMPLE 3 Synthesis of 4-(2-ethyl-[1,3]dioxan-2-yl)-2-methoxy-pyridine

To a stirred solution of 38.23 g of 1-(2-methoxy-pyridin-4-yl)-propan-1-one (231.4 mmol) as obtainable from Example 2 in 575 mL toluene were added 100 mL. 1,3-propandiol (1.39 mol, 6.0 eq), 473 μL sulfuric acid (4.63 mmol, 0.02 eq) and 889 mg para-toluene sulfonic acid monohydrate (4.63 mmol, 0.02 eq). The reaction mixture was heated for 72 h (NMR control: <2% starting material 1-(2-methoxy-pyridin-4-yl)-propan-1-one) to reflux using a Dean-Stark trap (oil bath temperature 160° C.). After cooling down to room temperature, 500 mL saturated aqueous NaHCO₃ were added and the phases were separated. The organic phase was washed twice with 250 mL, in total with 500 mL brine and was then dried over 50 g Na₂SO₄ (30 min) and filtered. The filter cake was washed with 100 mL toluene. After evaporation of solvent in a rotary evaporator (50° C./10 mbar), the crude product (40.31 g, 78% by weight) was obtained as a brown oil (HPLC purity 93.9% area). Purification was achieved using a high vacuum distillation (bp 95° C. at 0.056 mbar, oil bath temperature 125° C., 40 cm Vigreux column) furnishing the title compound (31.80 g, 142.4 mmol, 62% by weight) as colourless liquid.

Bp: 95° C. (0.056 mbar);

¹H NMR (300 MHz, CDCl₃): δ 8.19 (dd, 1H, J=5.2 Hz, J=0.8 Hz), 6.91 (dd, 1H, J=5.3 Hz, J=1.5 Hz), 6.78 (dd, 1H, J=1.4 Hz, J=0.8 Hz), 3.96 (s, 3H), 3.89 (m, 2H), 3.75 (m, 2H), 2.09 (m, 1H), 1.72 (q, 2H, J=7.5 Hz), 1.26 (m, 1H), 0.81 (t, 3H, J=7.5 Hz) ppm

EXAMPLE 4 Synthesis of 4-(2-ethyl-[1,3]dioxan-2-yl)-2-methoxy-pyridine-3-carbaldehyde

A stirred solution of 6.87 mL 2-bromomesitylene (44.78 mmol, 2.0 eq) in 44 mL THF was cooled to −45° C. 35.8 mL n-butyllithium in hexane (2.5 M, 89.56 mmol, 4.0 eq) were added within 20 min. The resulting white suspension was then allowed to warm to 0° C. within 2.5 h. At −10° C. the reaction mixture became a clear solution. Stirring was continued for an additional hour at 0° C. The solution was cooled to −10° C. and a solution of 5.00 g 4-(2-ethyl-[1,3]dioxan-2-yl)-2-methoxy-pyridine (22.39 mmol), as obtainable from Example 3, in 15 mL THF was added over 15 min under vigorous stirring. The resulting brown suspension was allowed to warm to 10° C. within 2.5 h. The cooling bath was then removed and stirring was continued at room temperature for an additional hour. The clear brown solution was then cooled to −23° C. and 5.19 mL DMF (67.17 mmol, 3.0 eq) were added. The mixture was allowed to slowly warm up to room temperature overnight. The reaction was quenched by addition of 100 mL saturated aqueous NH₄Cl. After 15 min, 50 mL water were added. The mixture was extracted three times with 150 mL, in total with 450 mL TBME. The combined organic phases were washed two times with 300 mL, in total 600 mL brine, dried over 20 g Na₂SO₄ (30 min) and filtered. The filter cake was washed with 40 mL TBME. After evaporation of solvent in a rotary evaporator (40° C./10 mbar), the crude product (12.048 g, 214% by weight) was obtained as a brown oil which was then purified by silica gel filtration (97 g silica gel) using a gradient elution with 2.0 L heptane/ethyl acetate (30:1) and 1.4 L heptane/ethyl acetate (5:1). Evaporation to dryness of the second fraction in a rotary evaporator (40° C./10 mbar) yielded the title compound (3.832 g, 15.2 mmol, 68% by weight).

¹H NMR (300 MHz, CDCl₃): δ 10.33 (s, 1H), 8.25 (d, 1H, J=5.5 Hz), 6.96 (d, 1H, J=5.3 Hz), 3.98 (s, 3H), 3.83 (m, 2H), 3.61 (m, 2H), 2.09 (m, 1H), 1.86 (q, 2H, J=7.5 Hz), 1.29 (m, 1H), 0.92 (t, 3H, J=7.5 Hz) ppm;

EXAMPLE 5 Synthesis of [4-(2-ethyl-[1,3]dioxan-2-yl)-2-methoxy-pyridin-3-yl]-methanol

To stirred solution of 3.178 g of 4-(2-ethyl-[1,3]dioxan-2-yl)-2-methoxy-pyridine-3-carbaldehyde as obtained from Example 4 (12.65 mmol) in 95 mL isopropanol and 15.8 mL water were added at 0° C. 134.6 mg sodium borohydride (3.416 mmol, 0.27 eq).

The reaction was monitored by HPLC, and after 30 min (<0.2% area starting material as obtained from Example 4), the reduction was quenched by addition of 11 mL acetone and stirring was continued for 30 min at room temperature. 190 mL saturated aqueous NH₄Cl were added and the mixture was extracted three times with 180 mL, in total with 540 mL to dichloromethane. The combined organic phases were dried over 20 g Na₂SO₄ (30 min) and filtered. The solid was washed with 40 mL dichloromethane. After evaporation of solvent in a rotary evaporator (40° C./10 mbar), the crude product (3.184 g, 99% by weight) was obtained as a yellow oil. Purification was achieved by trituration with 16 mL heptane for 24 h at room temperature and subsequent standing for 4 days at −20° C. After cold filtration and removement of residual solvent in a rotary evaporator (40° C./10 mbar), the title compound (2.827 g, 11.2 mmol, 88% by weight) was obtained as white crystals.

Mp: 79° C.;

¹H NMR (300 MHz, CDCl₃): δ 8.11 (d, 1H, J=5.3 Hz), 7.01 (d, 1H, J=5.3 Hz), 4.93 (d, 2H, J=6.6 Hz), 4.04 (s, 3H), 3.93 (m, 2H), 3.77 (m, 2H), 2.83 (t, 1H, J=7.2 Hz, 2.10 (m, 1H), 1.81 (q, 2H, J=7.5 Hz), 1.30 (m, 1H), 0.85 (t, 3H, J=7.4 Hz) ppm

EXAMPLE 6 Synthesis of 3-benzyloxymethyl-4-(2-ethyl-[1,3]dioxan-2-yl)-2-methoxy-pyridine

To a stirred solution of 3.828 g [4-(2-ethyl-[1,3]dioxan-2-yl)-2-methoxy-pyridin-3-yl]-methanol as obtained from Example 5 (15.11 mmol) in 21 mL THF were added within 10 min and at −78° C. 16.6 nth lithium bis(trimethylsilyl)amide in THF (1.0 M, 16.62 mmol, 1.1 eq). After additional 10 min at −78° C., stirring was continued for 10 rain at 0° C. and for 15 min at room temperature. 2.56 mL benzylbromide (21.15 mmol, 1.4 eq) and 570 mg tetrabutylammonium iodide (1.51 mmol, 0.1 eq) were subsequently added and the mixture was heated to 65° C. The reaction was monitored by HPLC. After 16 h at 65° C. (<2% area starting material as obtained from Example 5), 250 μL pyrrolidine (3.02 mmol, 0.2 eq) were added at room temperature. After 1 h at room temperature (<0.2% area starting material as obtained from Example 5), additional 625 μL pyrrolidine (3.02 mmol, 0.2 eq) were added. After 2.5 h (<0.1% area benzylbromide), the mixture was poured into 600 mL heptane and the organic phase was washed twice with 400 mL, in total with 800 mL aqueous HCl (0.5 M) and subsequently with 500 mL water. The organic phase was dried over 20 g Na₂SO₄ (30 min) and filtered. The solid was washed with 40 mL heptane. After evaporation of solvent in a rotary evaporator (40° C./10 mbar), the title compound (4.985 g, 96% by weight) was obtained as a yellow oil.

¹H NMR (300 MHz, CDCl₃): δ 8.12 (d, 1H, J=5.5 Hz), 7.25-7.41 (m, 5H), 6.98 (d, 1H, J=5.4 Hz), 4.73 (s, 2H), 4.63 (s, 2H), 3.98 (s, 3H), 3.85 (m, 4H), 2.09 (m, 1H), 1.80 (q, 2H, J=7.5 Hz), 1.24 (dm, 1H, J=13.0 Hz), 0.84 (t, 3H, J=7.4 Hz) ppm

EXAMPLE 7 Synthesis of 1-(3-benzyloxymethyl-2-methoxy-pyridin-4-yl)-propan-1-one

To stirred solution of 4.120 g 3-benzyloxymethyl-4-(2-ethyl-[1,3]dioxan-2-yl)-2-methoxy-pyridine as obtained from Example 6 (12.00 mmol) in 96 mL ethanol and 24 mL water were added at room temperature 461 mg para-toluenesulfonic acid monohydrate (2.40 mmol, 0.2 eq). The mixture was subsequently heated to 80° C. and the reaction was monitored by HPLC and after 6.25 h at 80° C. (<0.2% area starting material as obtained from Example 6), the solution was cooled down to room temperature and poured into 600 mL heptane. The organic phase was washed with 600 mL water, subsequently with 600 mL aqueous NaHCO₃ solution (0.1 M) and again with 600 mL water. The organic phase was dried over 20 g Na₂SO₄ (30 min) and filtered. The solid was washed with 40 mL heptane. After evaporation of solvent in a rotary evaporator (40° C./10 mbar), the title compound (3.302 g, 96% by weight) was obtained as a light yellow oil.

¹H NMR (300 MHz, CDCl₃): δ 8.14 (d, 1H, J=5.1 Hz), 7.29-7.37 (m, 5H), 6.75 (d, 1H, J=5.3 Hz), 4.62 (s, 2H), 4.50 (s, 2H), 3.95 (s, 3H), 2.74 (q, 2H, J=7.2 Hz), 1.06 (t, 3H, J=7.2 Hz) ppm

EXAMPLE 8 Synthesis of (4R,5S)-3-acetyl-4,5-diphenyl-oxazolidin-2-one

To a stirred suspension of 5.100 g (4R,5S)-(+)-cis-4,5-diphenyl-2-oxazolidinone (20.89 mmol) in 102 mL THF, were added 13.65 mL n-butyllithium in hexane (1.5 M, 20.47 mmol, 0.98 eq) at −78° C. during 6 min. The resulting dark red solution was stirred for additional 68 min at −78° C. During this period, the solution became colorless. Stirring was continued for 15 min at −25° C., before it was cooled again to −78° C. A solution of 1.536 mL acetyl chloride (21.31 mmol, 1.02 eq) in 15.3 mL THF was then added within 5 min. After 52 min, the mixture was poured on 510 mL water and the product was extracted three times with 305 mL, in total 915 mL dichloromethane. The combined organic phases were washed with 715 mL aqueous NaHCO₃ and with 715 mL brine. The solution was dried over 25 g sodium sulfate (30 min) and filtered. The filter cake was washed with 50 mL dichloromethane. After removal of solvent in a rotary evaporator (40° C., 30 mbar), the crude product (5.899 g, 100% by weight) was obtained as a white solid. Purification was accomplished by recrystallization from 13 mL toluene. The heterogeneous mixture was heated to reflux until a clear solution was obtained, which was then allowed to slowly cool down to room temperature. After two days, the title compound was collected by filtration as white crystals (5.157 g, 18.332 mmol, 88% by weight).

Mp: 142° C.;

¹H NMR (300 MHz, CDCl₃): δ 7.11 (m, 6H), 6.97 (m, 2H), 6.86 (m, 2H), 5.91 (d, 1H, J=7.5 Hz), 5.67 (d, 1H, J=7.5 Hz), 2.62 (s, 3H) ppm

EXAMPLE 9 Synthesis of (4R,5S)-3-[(R)-3-(3-benzyloxymethyl-2-methoxy-pyridin-4-yl)-3-hydrozy-pentanoyl]-4,5-diphenyl-oxazolidin-2-one

A 10 ml round bottomed flask was charged with 389.4 μL lithium bis(trimethylsilyl)amide solution (1.0 M in THF, 0.385 mmol, 1.1 eq) and the solution was cooled to −78° C. 108.4 mg (4R,5S)-3-acetyl-4,5-diphenyl-oxazolidin-2-one (0.385 mmol, 1.1 eq), as obtainable from Example 8, in 650 μL THF were slowly added (addition time: 5 min). During the addition, the color changed from colorless to bright yellow. After 2 h at −78° C., the solution was cooled to −95° C. and 100.0 mg 1-(3-benzyloxymethyl-2-methoxy-pyridin-4-yl)-propan-1-one (0.350 mmol), as obtainable from Example 7, dissolved in 400 μL THF were slowly added (addition time: 5 min). The solution was kept for additional 30 min at −95° C. and then for 45 min at −78° C. Subsequently, the reaction was quenched by addition of 5 mL aqueous 0.5 M HCl. The mixture was extracted three times with 10 mL, in total 30 mL dichloromethane and the combined extracts were dried over 1 g sodium sulfate (30 min) and filtered. The filter cake was washed with 2 mL dichloromethane. After removal of solvent in a rotary evaporator (40° C., 5 mbar), the title compound was obtained as a colorless oil (206.7 mg, 104% by weight, dr=92:8 (¹H-NMR).

Mp: 61° C.;

[α]_(D) ²⁰ (c=0.7417 g/dL, CHCl₃)=−23.9;

¹H NMR (300 MHz, CDCl₃): δ 7.99 (d, 1H, J=5.6 Hz), 6.83-7.33 (m, 15H), 6.57 (d, 1H, J=5.6 Hz), 5.79 (d, 1H, J=7.7 Hz), 5.51 (d, 1H, J=7.7 Hz), 5.31 (s, 1H), 4.89 (d, 1H, J=10.5 Hz), 4.81 (d, 1H, J=10.6 Hz), 4.42 (d, 1H, J=11.6 Hz), 4.35 (d, 1H, J=16.8 Hz), 4.33 (d, 1H, J=11.8 Hz), 3.90 (s, 3H), 3.22 (d, 1H, J=16.8 Hz), 1.92 (q, 2H, J=7.1 Hz), 0.80 (t, 3H, J=7.4 Hz) ppm

¹³C NMR (100 MHz, CDCl₃): δ 171.1, 163.8, 156.2, 153.6, 145.9, 138.5, 133.9, 132.6, 128.5, 128.3, 128.1, 128.1, 128.0, 127.9, 127.4, 126.3, 126.3, 117.8, 115.7, 80.3, 78.0, 71.9, 63.1, 62.7, 53.7, 46.0, 36.3, 7.8 ppm

EXAMPLE 10 Synthesis of (R)-3-(3-benzyloxymethyl-2-methoxy-pyridin-4-yl)-3-hydroxy-pentanoic acid

4.733 g (4R,5S)-3-acetyl-4,5-diphenyl-oxazolidin-2-one (16.82 mmol, 1.2 eq) as obtainable to from Example 8, were dissolved in 19 mL THF at 65° C. The solution was subsequently cooled to −78° C. and 17.00 mL lithium bis(trimethylsilyl)amide solution in THE (1.0 M, 16.82 mmol, 1.2 eq) were slowly added (addition time: 10 min). During the addition, the color changed from colorless to bright yellow. After 2 h at −78° C., the clear solution was cooled to −95° C. A solution of 4.000 g 1-(3-benzyloxymethyl-2-methoxy-pyridin-4-yl)-propan-1-one (14.02 mmol) as obtainable from Example 7, in 16 mL THE was slowly added (syringe pump, addition time: 30 min) and the solution was kept for additional 30 min at −95° C. and then for 45 min at −78° C. Subsequently, 87.6 mL aqueous LiOH solution (0.8 M, 70.1 mmol, 5.0 eq) and 7.01 mL aqueous H₂O₂ solution (10.0 M, 70.1 mmol, 5.0 eq) were added and stirring of the resulting suspension was continued at 0° C. for 30 min and at room temperature for 1 h. The precipitated auxiliary was collected by filtration and the solid was washed with 15 mL water. The filtrate was poured on 200 mL aqueous NaOH solution (2 M). A second portion of precipitated auxiliary was collected by filtration and the solid was washed with 3 mL water. The filtrate was then extracted 3 times with 200 mL, in total with 600 mL TBME in order to remove unreacted 1-(3-benzyloxymethyl-2-methoxy-pyridin-4-yl)-propan-1-one, unprecipitated auxiliary and several impurities. The aqueous phase was then acidified with aqueous HCl until pH 3. The resulting white suspension was extracted twice with 200 mL, in total 400 mL dichloromethane. The combined dichloromethane extracts were washed with 80 mL saturated aqueous NH₄Cl and 16 mL brine and were subsequently dried over 20 g sodium sulfate (30 min) and filtered. The solid was washed with 40 mL dichloromethane. After removal of solvent in a rotary evaporator (40° C., 5 mbar), the title compound was obtained as a light yellow oil (3.61 g, 75% by weight, er=87.2:12.8).

[α]_(D) ²⁰ (c=0.9884 g/dL, CHCl₃)=−23.3 (for ee=100%);

¹H NMR (300 MHz, CDCl₃): δ 8.08 (d, 1H, J=5.5 Hz), 7.35 (m, 5H), 6.78 (d, 1H, J=5.5 Hz), 6.16 (s, 1H), 4.97 (d, 1H, J=11.3 Hz), 4.86 (d, 1H, J=11.3 Hz), 4.65 (d, 1H, J=11.7 Hz), 4.60 (d, 1H, J=11.7 Hz), 3.93 (s, 3H), 2.96 (d, 1H, J=15.5 Hz), 2.84 (d, 1H, J=16.1 Hz), 1.86 (m, 2H), 0.76 (t, 3H, J=7.5 Hz) ppm;

¹³C NMR (100 MHz, CDCl₃): δ 173.7, 163.5, 155.3, 146.4, 137.2, 128.5, 128.4, 128.1, 128.1, 117.1, 115.7, 72.8, 63.2, 54.0, 46.3, 35.8, 7.9 ppm

EXAMPLE 11 Synthesis of (R)-5-ethyl-5-hydroxy-2,5,6,9-tetrahydro-8-oxa-2-aza-benzocycloheptene

To a stirred solution of 3.00 g (R)-3-(3-benzyloxymethyl-2-methoxy-pyridin-4-yl)-3-hydroxy-pentanoic acid (8.69 mmol), as obtainable from Example 10, in 11 mL 1,2-dimethoxyethane, were added 2.01 mL aqueous HBr (48%) (17.89 mmol, 2.06 eq). After 15 min at room temperature, the solution was heated to 50° C. After 4 h, the first product crystals appeared. The reaction was monitored by HPLC. After 24 h at 50° C. (<1% area (R)-3-(3-benzyloxymethyl-2-methoxy-pyridin-4-yl)-3-hydroxy-pentanoic acid), the reaction was cooled to room temperature. The mixture was allowed to stir at room temperature for 72 h and was then filtered. The solid was washed twice with 2.24 mL, in total with 4.48 mL TBME, and subsequently with 2.24 mL acetone; twice with 2.24 mL, in total with 4.48 mL water, and finally twice with 2.24 mL, in total with 4.48 mL acetone. After drying in vacuo, the title compound (1.040 g, 4.66 mmol, 54% by weight) was obtained as white crystals, and in an enantiomeric ratio of er=99.95:0.05 as determined by the following Chiral HPLC method:

Method 75ODH2.M Sample preparation ethanol solution Equipment Agilent 1100 Column Chiralcel-ODH, 250 × 4.6, Nr. DB075 Temperature 25° C. Mobile phase 75% heptane, 25% ethanol/trifluoroacetic acid (99:1) Flow 0.8 mL/min Injection volume 5 μL Detection UV 308 nm Retention time 9.68 win(S)-product; 13.28 min(R)-product

Mp>270° C. (decomposition);

[α]_(D) ²⁰ (c=1.1000 g/dL, DMSO)=+134.4;

¹H NMR (300 MHz, DMSO): δ 11.67 (br. s, 1H), 7.34 (d, 1H, 7.2 Hz), 6.33 (d, 1H, 7.2 Hz), 5.72 (br. s, 1H), 5.34 (d, 1H, J=15.1 Hz), 5.21 (d, 1H, J=15.1 Hz), 3.32 (d, 1H, J=13.5 Hz), 2.98 (d, 1H, J=13.7 Hz), 1.68 (m, 2H), 0.80 (t, 3H, J=7.5 Hz) ppm;

¹³C NMR (100 MHz, DMSO): δ 171.9, 161.1, 155.6, 133.7, 122.6, 104.9, 72.7, 61.0, 42.2, 35.7, 8.1 ppm

EXAMPLE 12 Synthesis of 2-chloro-N-isopropyl-isonicatinamide

To a stirred suspension of 20.00 g 2-chloroisonicotinic acid (123.2 mmol) in 200 mL acetonitrile were added 11.77 mL thionyl chloride (160.2 mmol, 1.3 eq) and 762 μL DMF (9.86 mmol, 0.08 eq). The mixture was heated to reflux and was monitored by HPLC. After 60 min (<1% of 2-chloroisonicotinic acid), the reaction mixture was cooled to room temperature and all volatiles were removed in a rotary evaporator (40° C./10 mbar). The residual oil was dissolved in 200 mL dichloromethane and the solution was cooled to 0° C. 20.6 mL triethylamine (147.8 mmol, 1.20 eq) and 11.7 mL isopropylamine (135.5 mmol, 1.10 eq) were subsequently added and stirring was continued for 2 h at 0° C. until the solution turned almost black. The mixture was poured on 200 mL water and phases were separated. The organic phase was washed with 200 mL brine, dried over 15 g sodium sulfate and filtered. The filter cake was washed with 30 mL dichloromethane. After removal of solvent in a rotary evaporator (40° C., 20 mbar), the crude product (24.83 g, 102% w/w) was obtained as a brown solid (HPLC purity 98.6% area).

Mp: 99° C. (decomp.);

¹H NMR (300 MHz, CDCl₃): δ 8.50 (dd, 1H, J=4.9 Hz, J=0.6 Hz), 7.62 (dd, 1H, J=1.3 Hz, J=0.6 Hz), 7.51 (dd, 1H, J=5.1 Hz, J=1.5 Hz), 5.94 (br. s, 1H), 4.27 (m, 1H), 1.28 (d, 6H, J=6.6 Hz) ppm;

¹³C NMR (100 MHz, CDCl₃): δ 163.4, 152.4, 150.4, 145.1, 122.0, 119.8, 42.5, 22.6 ppm.

EXAMPLE 13 Synthesis of N-isopropyl-2-methoxy-isonicotinamide

To a stirred solution of 19.44 g 2-chloro-N-isopropyl-isonicotinamide (97.86 mmol) as obtainable from example 12, in 165 mL methanol were added 27.82 g NaOMe (489.3 mmol, 5.0 eq) in four equal portions over 60 min. The solution was then heated to 80° C. and the reaction was monitored by HPLC. After 23 h (<2% area starting material 2-chloro-N-isopropyl-isonicotinamide), the mixture was cooled to room temperature and quenched by addition of 200 mL saturated aqueous NH₄Cl. The product was extracted three times with 150 mL, in total 450 mL dichloromethane. The combined organic phases were dried over 40 g Na₂SO₄ (30 min) and filtered. The filter cake was washed with 80 mL dichloromethane. After removal of solvent in a rotary evaporator (40° C., 22 mbar), the crude product (15.856 g, 83% w/w, HPLC purity 93.7% area) was obtained as a white solid.

Mp: 100° C.

¹H NMR (300 MHz, CDCl₃): δ 8.24 (dd, 1H, J=5.3 Hz, J=0.6 Hz), 7.15 (dd, 1H, J=5.3 Hz, J=1.3 Hz), 7.02 (dd, 1H, J=1.3 Hz, J=0.6 Hz), 5.89 (br. s, 1H), 4.28 (m, 1H), 3.96 (s, 3H), 1.26 (d, 6H, J=6.6 Hz) ppm;

¹³C NMR (100 MHz, CDCl₃): δ 165.34, 165.26, 148.3, 145.6, 114.5, 109.1, 54.3, 42.7, 23.2 ppm.

EXAMPLE 14 Synthesis of 3-hydroxy-2-isopropyl-4-methoxy-2,3-dihydro-pyrrolo[3,4-c]pyridin-1-one

To a stirred suspension of 10.00 g N-isopropyl-2-methoxy-isonicotinamide (51.40 mmol), as obtainable from example 13, in 300 mL TBME were added at room temperature 17.2 mL TMEDA (113.3 mmol, 2.2 eq) resulting in the formation of a clear solution, which was then cooled to −78° C. Subsequently 102.8 mL n-butyllithium in hexane (1.5 M, 154.4 mmol, 3.0 eq) were then added over 35 min and stirring was continued at the same temperature for additional 3 h min and subsequently at −22° C. for another 3 h. To the slightly brown suspension, 13.9 mL DMF (180.0 mmol, 3.5 eq) were added at −28° C. The resulting suspension was quenched after 16 h 45 min by addition of 200 mL saturated aqueous NH₄Cl. The mixture was extracted three times with 150 mL, in total 450 mL dichloromethane. The combined organic phases were dried over 20 g Na₂SO₄ (30 min) and filtered. The filter cake was washed with 40 mL dichloromethane. After evaporation of solvent in a rotary evaporator (40° C./20 mbar), the crude product (19.400 g, 170% w/w, regioselectivity:11.68:1, as determined by ¹H-NMR) was obtained as a brown oil (HPLC purity 77.6%).

Mp 117° C.;

¹H NMR (300 MHz, CDCl₃): δ 8.33 (d, 1H, J=5.1 Hz), 7.26 (dd, 1H, J=5.1 Hz), 6.05 (d, 1H, J=7.5 Hz), 4.40 (sept, 1H, J=6.8 Hz), 4.07 (s, 3H), 2.44 (d, 1H, J=8.5 Hz), 1.44 (d, 3H, J=6.8 Hz), 1.42(d, 3H, J=6.8 Hz) ppm;

¹³C NMR (100 MHz, CDCl₂): δ 165.3, 159.3, 149.2, 143.1, 124.6, 110.8, 79.9, 53.9, 44.4, 21.8, 20.1 ppm.

EXAMPLE 15 Synthesis of 4-methoxy-3H-furo[3,4-c]pyridin-1-one

To a stirred solution of 19.40 g crude 3-hydroxy-2-isopropyl-4-methoxy-2,3-dihydro-pyrrolo[3,4-c]pyridin-1-one (87.29 mmol), as obtainable from example 14, in 300 mL isopropanol and 100 mL water were added at room temperature 5.160 g NaBH₄ (130.9 mmol, 1.5 eq). After 3 h (<1.0% area 3-hydroxy-2-isopropyl-4-methoxy-2,3-dihydro-pyrrolo[3,4-c]pyridin-1-one), the reduction was quenched at 0° C. by addition of 34.0 mL acetone (474.4 mmol, 5.3 eq) and stirring was continued for 35 min at room temperature. The mixture was poured on 415 mL aqueous HCl (2.0 M, 829.3 mmol, 9.5 eq) at 0° C. and stirring was continued for 20 min at room temperature. The mixture was then heated to 50° C. overnight and was subsequently cooled to 0° C. Dipotassium hydrogen phosphate was added in order to adjust pH 3.0 and ca. 95% of the isopropanol were removed in a rotary evaporator (40° C./10 mbar). Water was added until the salts were dissolved and the mixture was extracted three times with 300 mL, in total 900 mL dichloromethane. The combined organic phases were dried over 50 g Na₂SO₄ (30 min) and filtered. The solid was washed with 100 mL dichloromethane. After evaporation of solvent in a rotary evaporator (40° C./25 mbar), the crude product (9.963 g, 69% w/w) was obtained as a light brown solid (HPLC purity 80.7% area). Purification was achieved by trituration with 30 mL ethyl acetate for 24 h at room temperature and subsequent addition of 60 mL heptane. The suspension was then allowed to stand for 24 h at 5° C. yielding the title product (5.486 g, 33.22 mmol, 40% w/w (68% over 2 steps), HPLC purity 95.1% area) as a beige solid.

Mp: 90° C.;

¹H NMR (300 MHz, CDCl₃): δ 8.35 (d, 1H, J=5.1 Hz), 7.36 (d, 1H, J=5.3), 5.29 (s, 2H), 4.07 (s, 3H) ppm;

¹³C NMR (100 MHz, CDCl₃): δ 169.6, 159.3, 148.1, 136.3, 129.0, 111.7, 68.1, 54.0 ppm.

EXAMPLE 16 Synthesis of 1-ethyl-4-methoxy-1,3-dihydro-furo[3,4-c]pyridin-1-ol

To 10.52 mL triethylaluminum in toluene (1.9 M, 19.99 mmol, 1.1 eq) were added dropwise 39.97 mL ethyllithium in cyclohexane/benzene (0.5 M, 19.99 mmol, 1.1 eq) at 0° C. After 15 min at 0° C., 50.5 mL THF (precooled to −40° C.), were added rapidly via a canula. A solution of 3.0 g 4-methoxy-3H-furo[3,4c]pyridin-1-one (18.17 mmol), as obtainable from example 15, in 75 mL THF was subsequently added rapidly at −40° C. After 10 min at −40° C., additional 39.97 mL ethyllithium in cyclohexane/benzene (0.5 M, 19.99 mmol, 1.1 eq) were added slowly. The mixture was allowed to warm up to −15° C. within 3 h and the reaction was afterwards quenched by addition of 3.68 mL methanol (100 mmol, 5 eq). After 30 min, the mixture was poured in 1.5 L saturated aqueous potassium sodium tartrate and was extracted three times with 500 mL, in total with 1.5 L dichloromethane. The combined organic phases were dried over 100 g Na₂SO₄ (30 min) and filtered. The solid was washed with 200 mL dichloromethane. After evaporation of solvent in a rotary evaporator (40° C./10 mbar), the crude product (3.77 g, 106% w/w) was obtained as a brown oil (HPLC purity 51.5% area), which was purified by column chromatography with heptane/ethyl acetate (7:3) yielding the title product (1.877 g, 9.61 mmol, 53% w/w; HPLC purity 97.9% area; ratio lactol/hydroxy-ketone=6:1 by NMR) as yellow oil.

Mp: 145° C.

¹H NMR (300 MHz, CDCl₃): lactol-form: δ 8.15 (d, 1H, J=5.3 Hz), 6.90 (d, 1H, J=5.2 Hz), 5.13 (d, 1H, J=13.2 Hz), 4.95 (d, 1H, J=13.2 Hz), 3.99 (s, 3H), 2.86 (s, 1H), 2.06 (m, 2H), 0.86 (t, 3H, J=7.4 Hz) ppm;

hydroxy-ketone-form: δ 8.21 (d, 1H, J=5.3 Hz), 6.99 (d, 1H, J=5.2 Hz), 4.63 (d, 2H, J=7.2 Hz), 4.00 (s, 3H), 3.07 (t, 1H, J=7.1 Hz), 2.92 (q, 2H, J=7.1 Hz), 1.21 (t, 3H, J=7.1 Hz) ppm;

¹³C NMR (100 MHz, CDCl3): lactol-form: δ 159.9, 151.9, 146.9, 121.6, 110.7, 110.6, 69.4, 53.5, 32.2, 8.0 ppm.

EXAMPLE 17 Synthesis of 1-[3-(tert-Butyl-dimethyl-silanyloxymethyl)-2-methoxy-pyridin-4-yl]-propan-1-one

To a solution of 1.500 g 1-ethyl-4-methoxy-1,3-dihydro-furo[3,4-c]pyridin-1-ol (7.68 mmol) as obtainable from example 16, and 1.831 g imidazole (26.89 mmol, 3.5 eq) in 12.5 mL DMF were added 3.475 g TBSCl (23.05 mmol, 3.0 eq) at 0° C. The solution was allowed to slowly warm up to room temperature overnight until less than 0.1% area 1-ethyl-4-methoxy-1,3-dihydro-furo[3,4-c]pyridin-1-ol were achieved, as detected by HPLC. 285 mL heptane and 444 mL water were added. The organic phase was separated, dried over 20 g Na₂SO₄ (30 min) and filtered. The solid was washed with 40 mL heptane.

After evaporation in a rotary evaporator (40° C./10 mbar) and subsequently under high vacuum (40° C., 0.01 mbar), the title product (2.34 g, 7.56 mmol, 98% w/w) was obtained as a light yellow oil (HPLC purity 99.0% area).

¹H NMR (300 MHz, CDCl₃): δ 8.11 (d, 1H, 5.1 Hz), 6.72 (d, 1H, J=5.2 Hz), 4.77 (s, 2H), 3.96 (s, 3H), 2.82 (t, 2H, J=7.1 Hz), 1.16 (t, 3H, J=7.2 Hz), 0.88 (s, 9H), 0.07 (s, 3H), 0.00 (s, 3H) ppm;

¹³C NMR (100 MHz, CDCl₃): δ 205.1, 160.2, 149.2, 144.8, 118.6, 112.9, 56.3, 52.7, 35.4, 24.9, 17.6, 6.7, −6.6 ppm.

EXAMPLE 18 Synthesis of (R)-3-{3-[3-(tert-butyl-dimethyl-silanyloxymethyl)-2-methoxy-pyridin-4-yl]-3-hydroxy-pentanoyl}-4-phenyl-oxazolidin-2-one

A suitable reaction flask was charged with 9.79 mL lithium bis(trimethylsilyl)amide solution (1.0 Min THF, 9.69 mmol, 3.0 eq) and the solution was cooled to −78° C. 1.989 g (R)-3-acetyl-4-phenyl-oxazolidin-2-one (9.69 mmol, 3.0 eq), as obtainable from example 21, in 7.5 mL THF were slowly added (ca. 10 min). After 2 h at −78° C., the solution was cooled to −95° C. and 1.000 g 1-[3-(tert-Butyl-dimethyl-silanyloxymethyl)-2-methoxy-pyridin-4-yl]-propan-1-one (3.231 mmol), as obtainable from example 17, dissolved in 6.7 mL THF were slowly added (ca. 60 min) using a syringe pump. The solution was kept for additional 30 min at −95° C. and then for 1 h at −78° C. Subsequently, the reaction was quenched by addition of 50 mL aqueous 0.5 M HCl. The mixture was extracted three times with 50 mL, in total 150 mL dichloromethane and the combined extracts were dried over 10 g Na₂SO₄ (30 min) and filtered. The filter cake was washed with 20 mL dichloromethane. After removal of solvent in a rotary evaporator (40° C., 5 mbar), the crude product was obtained as an orange solid (3.12 g, 188% w/w, dr=87:13 (calculated by ¹H-NMR), HPLC purity 37.8% area). An analytical sample (dr>50:1; HPLC purity 100% area, colorless oil) was obtained by semipreparative HPLC.

[α]_(D) ²⁰ (c=0.285 g/dL, CHCl₃)=−98.1;

¹H NMR (300 MHz, CDCl₃): δ 7.90 (d, 1H, J=5.4 Hz), 7.23 (m, 3H), 7.03 (m, 2H), 6.67 (d, 1H, J=5.5 Hz), 5.42 (s, 1H), 5.35 (dd, 1H, J=8.7 Hz, J=4.0 Hz), 4.97 (d, 1H, J=11.6 Hz), 4.93 (d, 1H, J=11.6 Hz), 4.62 (t, 1H, J=8.7 Hz), 4.18 (dd, 1H, J=8.6 Hz, J=4.2 Hz), 4.07 (d, 1H, J=16.2 Hz), 3.91 (s, 3H), 3.23 (d, 1H, J=16.2 Hz), 1.90 (m, 2H), 0.87 (s, 9H), 0.78 (t, 3H, J=7.4 Hz), 0.06 (s, 3H), 0.01 (s, 3H) ppm;

¹³C NMR (100 MHz, CDCl₃): δ 170.6, 162.8, 155.4, 153.7, 145.3, 138.4, 129.0, 128.4, 125.4, 120.3, 115.5, 78.1, 69.8, 57.5, 56.5, 53.5, 46.0, 36.4, 25.9, 18.3, 7.9, −5.3, −5.4 ppm.

EXAMPLE 19 Synthesis of (R)-3-hydroxy-3-(3-hydroxymethyl-2-methoxy-pyridin-4-yl)-pentanoic acid

To a solution of 3.11 g (R)-3-{3-[3-(tert-butyl-dimethyl-silanyloxymethyl)-2-methoxy-pyridin-4-yl]-3-hydroxy-pentamoyl}-4-phenyl-oxazolidin-2-one (6.04 mmol), as obtainable from example 18, in 35 mL THF were added at 0° C. 37.8 mL aqueous LiOH solution (0.8 M, 30.2 mmol, 5.0 eq) and 3.02 mL aqueous H₂O₂ solution (10.0 M, 30.2 mmol, 5.0 eq). After 30 min, 220 mL aqueous NaOH solution (2 M) were added and the ice bath was removed. The reaction was monitored by HPLC. After 2 h (<0.2% area (R)-3-{3-[3-(tert-butyl-dimethyl-silanyloxymethyl)-2-methoxy-pyridin-4-yl]-3-hydroxy-pentanoyl}-4-phenyl-oxazolidin-2-one), the resulting emulsion was extracted 7 times with 100 mL, in total 700 mL TBME. The aqueous phase was acidified with aqueous HCl in order to adjust is pH 3.0 and extracted nine times with 100 mL, in total 900 mL dichloromethane/ethanol (4:1). After evaporation in a rotary evaporator (40° C., 5 mbar), the title product was obtained as a colorless semisolid (700 mg, 2.74 mmol, yield of 45% w/w, or 85% when calculated over the two steps) and in a purity of 89.2% as determined by HPLC (er=80.47:19.53, see Chiral HPLC method below).

Chiral HPLC Method:

Method 90ADH1.M Sample ethanol solution preparation Equipment Agilent 1100 Column Chiralpak-ADH, 250 × 4.6, Nr. DB078 Temperature 25° C. Mobile phase 90% heptane, 10% ethanol/trifluoroacetic acid (99:1) Flow 0.8 mL/min Injection volume 5 μL Detection UV 308 nm

Retention time: 22.20 min for (R)-3-{3-[3-(tert-butyl-dimethyl-silanyloxymethyl)-2-methoxy-pyridin-4-yl]-3-hydroxy-pentanoyl}-4-phenyl-oxazolidin-2-one; and 24.78 min for (S)-3-{3-[3-(tert-butyl-dimethyl-silanyloxymethyl)-2-methoxy-pyridin-4-yl]-3-hydroxy-pentanoyl}-4-phenyl-oxazolidin-2-one.

[α]_(D) ²⁰ (c=1.3154 g/dL, CHCl₃)=+9.1;

¹H NMR (300 MHz, CDCl₃): δ 8.03 (d, 1H, J=5.5 Hz), 6.76 (d, 1H, J=5.4 Hz), 5.04 (d, 1H, J=12.2 Hz), 4.89 (d, 1H, J=12.2 Hz), 3.97 (s, 3H), 3.07 (d, 1H, J=16.2 Hz), 2.85 (d, 1H, J=16.2 Hz), 1.92 (br. q, 2H, J=7.5), 0.82 (t, 3H, J=7.4 Hz) ppm;

¹³C NMR (100 MHz, CDCl₃): δ 175.6, 163.5, 154.2, 145.5, 120.9, 115.3, 77.4, 56.5, 54.1, 44.7, 35.3, 8.1 ppm.

EXAMPLE 20 Synthesis of (R)-5-ethyl-5-hydroxy-2,5,6,9-tetrahydro-8-oxa-2-aza-benzocycloheptene

To a stirred solution of 1.097 g (R)-3-hydroxy-3-(3-hydroxymethyl-2-methoxy-pyridin-4-yl)-pentanoic acid (4.298 mmol) as obtainable from example 19, in 15.1 mL 1,2-dimethoxyethane, were added 1.014 mL aqueous HBr (48%) (9.03 mmol, 2.1 eq). After 15 min at room temperature, the solution was heated to 50° C. After 18 h at 50° C., the resulting suspension was allowed to stir at room temperature for additional 24 h and subsequently to stand at 5° C. for 18 h. The precipitate was collected by filtration using no vacuum and was subsequently washed twice with 2.55 mL, in total with 5.1 mL TBME, then with 2.55 mL acetone, two times with 3.18 mL, in total with 6.36 mL water and finally two times with 3.18 mL, in total with 6.36 mL acetone. After evaporation of residual solvent in a rotary evaporator (40° C./10 mbar), the title compound was obtained as white crystals (418.1 mg, 1.873 mmol, 44% w/w), in high purity (HPLC purity 100% area), and in an enantiomeric ratio of er=100.00:0.00 (see chiral HPLC method below).

Chiral HPLC Method:

Method 75ODH2.M Sample ethanol solution preparation Equipment Agilant 1100 Column Chiralcel-ODH, 250 × 4.6, Nr. DB075 Temperature 25° C. Mobile phase 75% heptane, 25% ethanol/trifluoroacetic acid (99:1) Flow 0.8 mL/min Injection volume 5 μL Detection UV 308 nm

Retention time: 9.68 min for (S)-5-ethyl-5-hydroxy-2,5,6,9-tetrahydro-8-oxa-2-aza-benzocycloheptene; and 13.28 min for (R)-5-ethyl-5-hydroxy-2,5,6,9-tetrahydro-8-oxa-2-aza-benzocycloheptene.

[α]_(D) ²⁰ (c=1.178 g/dL, DMSO)=+127.9;

Mp>270° C. (decomp.);

¹H NMR (300 MHz, DMSO): δ 11.67 (br. s, 1H), 7.34 (d, 1H, 7.2 Hz), 6.33 (d, 1H, 7.2 Hz), 5.72 (br. S, 1H), 5.34 (d, 1H, J=15.1 Hz), 5.21 (d, 1H, J=15.1 Hz), 3.32 (d, 1H, J=13.5 Hz), 2.98 (d, 1H, J=13.7 Hz), 1.68 (m, 2H), 0.80 (t, 3H, J=7.5 Hz) ppm;

all other analytical data are in accordance with those described in example 11.

EXAMPLE 21 Synthesis of (R)-3-acetyl-4-phenyl-oxazolidin-2-one

To a stirred suspension of 5.000 g (4R)-(−)-4-phenyl-2-oxazolidinone (30.03 mmol) in 100 ml, THF, were added 21.0 mL n-butyllithium in hexane (1.5 M, 31.53 mmol, 1.05 eq) at 0° C. within 10 min. The resulting colorless solution was stirred for additional 50 min at 0° C. 2.57 mL acetyl chloride (36.04 mmol, 1.2 eq) were then added within 1 min. After 3.5 h the reaction was stopped by addition of 25 mL saturated aqueous NH₄Cl and the mixture was extracted with 75 mL ethyl acetate. The organic phase was washed with 50 mL saturated aqueous NaHCO₃ and with 50 mL brine. The solution was dried for 30 minutes over 5 g Na₂SO₄ and filtered. The filter cake was washed with 10 mL ethyl acetate. After removal of solvent in a rotary evaporator (40° C., 18 mbar), the crude product was obtained as white crystals (6.13 g, 100% w/w; HPLC purity 88.3% area). Further purification was achieved by dissolving in 10.6 mL ethyl acetate at reflux temperature and subsequent dropwise addition of 26.6 mL heptane. The resulting suspension was allowed to slowly cool down to 5° C. and after standing overnight, the precipitate was collected by filtration. After washing with 3 mL heptane, the title compound was obtained as white crystals (5.26 g, 25.6 mmol, 85% by weight) and in high purity (HPLC purity 96.6% area).

[α]_(D) ²⁰ (c=0.083 g/dL, CHCl₃)=−58.8;

Mp: 94° C.;

¹H NMR (300 MHz, CDCl₃): δ 7.25-7.42 (m, 5H), 5.42 (dd, 1H, J=8.8 Hz, J=3.5 Hz), 4.69 (t, 1H, J=8.8 Hz), 4.29 (dd, 1H, J=8.8 Hz, J=3.5 Hz), 2.53 (s, 3H) ppm;

¹³C NMR (100 MHz, CDCl₃): δ 169.7, 153.9, 139.1, 129.2, 128.8, 126.0, 70.0, 57.5, 23.8 ppm. 

1-17. (canceled)
 18. A process for the production of a compound of formula (I), wherein said compound of formula (I)

or a pharmaceutically acceptable salt or ester thereof, wherein R and R¹ are independently, alkyl or benzyl, which benzyl is optionally substituted by one, two or three substituents including —O-alkyl; alkyl or halogen; with the proviso that: if R is alkyl, R¹ in formula (I) may also be hydrogen or silyl, and R¹ in formula (II) may also be silyl; R² is hydrogen or halogen; is converted into a compound of formula (D)

by: a) converting said compound of formula (I) into a compound formula (A)

in the presence of a mineral acid and an ethereal solvent at temperatures between room temperature (RT) and 60° C.; and b) further reacting said compound of formula (A) with a compound of formula (B)

in the presence of diisopropyl azodicarboxylate (DIAD), ethyldiphenylphosphine (EtPPh₂) and dimethylacetamide (DMA), to give a compound of formula (C)

and c) said compound of formula (C) is further reacted in the presence of palladium (II) acetate (Pd(OAc)₂), potassium acetate (KOAc), triphenylphosphine (Ph₃P), tetrabutyl ammonium bromide (Bu₄NBr) and acetonitrile (MeCN) to give the corresponding compound of formula (D)

wherein R² is defined in claim 1; R⁸ and R⁹ are independently alkyl or halogen; and R¹⁰ is 4-methyl-piperidin-1-ylmethyl or hydrogen.
 19. The process according to claim 18, wherein R² and R¹⁰ are both hydrogen, and R⁸ and R⁹ are both fluorine.
 20. The process according to claim 18, wherein R² is hydrogen, R¹⁰ is 4-methyl-piperidin-1-ylmethyl, R⁸ is chlorine and R⁹ is methyl.
 21. The process according to claim 18, wherein the process step a) is carried out in the presence of hydrobromic acid (HBr) and dimethoxyethane (DME) at temperatures between 45 and 55° C.
 22. A compound of general formula (I)

wherein R and R¹ are independently alkyl or benzyl, which benzyl is optionally substituted by —O-alkyl; alkyl or halogen; and R² is hydrogen or halogen.
 23. The compound of formula (I) according to claim 22, which is (R)-3-(3-benzyloxymethyl-2-methoxy-pyridin-4-yl)-3-hydroxy-pentanoic acid.
 24. A process for converting a compound of formula (I) as claimed in claim 22 into a compound of formula (D)

said process comprising the steps of: a) converting said compound of formula (I) into a compound formula (A)

in the presence of a mineral acid and an ethereal solvent at temperatures between room temperature (RT) and 60° C.; and b) further reacting said compound of formula (A) with a compound of formula (B)

in the presence of diisopropyl azodicarboxylate (DIAD), ethyldiphenylphosphine (EtPPh₂) and dimethylacetamide (DMA), to give a compound of formula (C)

and c) further reacting said compound of formula (C) in the presence of palladium (II) acetate (Pd(OAc)₂), potassium acetate (KOAc), triphenylphosphine (Ph₃P), tetrabutyl ammonium bromide (Bu₄NBr) and acetonitrile (MeCN) to give the corresponding compound of formula (D)

wherein; R⁸ and R⁹ are independently alkyl or halogen; and R¹⁰ is 4-methyl-piperidin-1-ylmethyl or hydrogen.
 25. The process of claim 24, wherein the compound of formula (I) is

and the compound produced is:


26. A process for the preparation of the compounds of formula (I) according to claim 22 comprising: a) reacting a compound of formula (II),

with a compound of formula (III),

and b) further reacting in the presence of alkali- or earth alkali metal hydroxides to give the compounds of formula (I), wherein R and R¹ are independently, alkyl or benzyl, which benzyl is optionally substituted by —O-alkyl; alkyl or halogen; R² is hydrogen or halogen; X is

R³ and R⁴ are hydrogen, phenyl, alkyl or —C(CH₃)₂-phenyl; R⁵ is phenyl, benzyl or alkyl; R⁶ is hydrogen, alkyl or phenyl; and R⁷ is hydrogen, methyl or phenyl; or alternatively R⁵ and R⁶, together with the carbon atoms to which they are attached form an indan moiety and R⁷ is hydrogen; R¹¹ and R¹² are independently alkyl, cycloalkyl, benzyl or phenyl; and R¹³ is phenyl or alkyl.
 27. The process of claim 18, wherein the compound of formula (D) is:


28. A compound prepared by a process according to claim
 18. 29. (canceled) 